Merge pull request swiftlang#59073 from compnerd/5.7-unarch

[5.7] Frontend: add an additional search path for swift modules

Author: compnerd

lib/Frontend/CompilerInvocation.cpp

@@ -188,7 +188,15 @@ static void updateRuntimeLibraryPaths(SearchPathOptions &SearchPathOpts,
     LibPath = SearchPathOpts.getSDKPath();
     llvm::sys::path::append(LibPath, "usr", "lib", "swift");
     if (!Triple.isOSDarwin()) {
+      // Use the non-architecture suffixed form with directory-layout
+      // swiftmodules.
       llvm::sys::path::append(LibPath, getPlatformNameForTriple(Triple));
+      RuntimeLibraryImportPaths.push_back(std::string(LibPath.str()));
+
+      // Compatibility with older releases - use the architecture suffixed form
+      // for pre-directory-layout multi-architecture layout.  Note that some
+      // platforms (e.g. Windows) will use this even with directory layout in
+      // older releases.
       llvm::sys::path::append(LibPath, swift::getMajorArchitectureName(Triple));
     }
     RuntimeLibraryImportPaths.push_back(std::string(LibPath.str()));